APOD: A High Cliff on Comet... (2021 Nov 28)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4647
Joined: Fri Dec 04, 2009 3:27 am

APOD: A High Cliff on Comet... (2021 Nov 28)

Post by APOD Robot » Sun Nov 28, 2021 5:11 am

Image A High Cliff on Comet Churyumov-Gerasimenko

Explanation: This high cliff occurs not on a planet, not on a moon, but on a comet. It was discovered to be part of the dark nucleus of Comet Churyumov-Gerasimenko (CG) by Rosetta, a robotic spacecraft launched by ESA that rendezvoused with the Sun-orbiting comet in 2014. The ragged cliff, as featured here, was imaged by Rosetta in 2014. Although towering about one kilometer high, the low surface gravity of Comet CG would likely make it an accessible climb -- and even a jump from the cliff survivable. At the foot of the cliff is relatively smooth terrain dotted with boulders as large as 20 meters across. Data from Rosetta indicates that the ice in Comet CG has a significantly different deuterium fraction -- and hence likely a different origin -- than the water in Earth's oceans. Rosetta ended its mission with a controlled impact onto Comet CG in 2016. Comet CG has just completed another close approach to Earth and remains visible through a small telescope.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
orin stepanek
Plutopian
Posts: 7435
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by orin stepanek » Sun Nov 28, 2021 1:09 pm

300px-Comet_67P_on_19_September_2014_NavCam_mosaic.jpg
cometcliffs_RosettaAtkinson_960.jpg
Comet Churyumov-Gerasimenko; The Comet looks
like a ferocious beast to me :mrgreen: ! The rugged terrain
makes it look look like it was torn off from a mountain
of some planet! 🤪 I think the ice looks like fallen snow!
8-) Just my vivid imagination worki8ng OT!
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

E Fish
Science Officer
Posts: 131
Joined: Thu Mar 09, 2017 2:29 pm

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by E Fish » Sun Nov 28, 2021 3:54 pm

and even a jump from the cliff survivable.
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff. :shock:

User avatar
Chris Peterson
Abominable Snowman
Posts: 16596
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Chris Peterson » Sun Nov 28, 2021 4:18 pm

E Fish wrote: Sun Nov 28, 2021 3:54 pm
and even a jump from the cliff survivable.
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff. :shock:
From the base, a jump of less than a meter per second would take you right to the top, and then you'd fall back down, landing at that same low speed. (FWIW, you hit the ground at about 1 m/s when you fall from a height of 5 cm!)
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Jim Armstrong

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Jim Armstrong » Sun Nov 28, 2021 4:51 pm

This (or the other one) is one of my favorite APOD images.

DL MARTIN

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by DL MARTIN » Sun Nov 28, 2021 5:39 pm

Thanks for qualifying for me what a comet actually looks like. I grew up thinking it was just a ball of ice that shed crystals as it encountered the heat from the Sun - thus the tail.

User avatar
Chris Peterson
Abominable Snowman
Posts: 16596
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Chris Peterson » Sun Nov 28, 2021 5:57 pm

DL MARTIN wrote: Sun Nov 28, 2021 5:39 pm Thanks for qualifying for me what a comet actually looks like. I grew up thinking it was just a ball of ice that shed crystals as it encountered the heat from the Sun - thus the tail.
Some are. They range from dirty snowballs to snowy dirtballs. Pristine comets making their first pass are probably close to what you imagined. Those that are in short period orbits and have made many orbits are more like asteroids. Some have lost all of their volatiles and can only be distinguished from asteroids by their orbits (sometimes).

(And, of course, their mass is important in determining just how regular or irregular their shape is. High mass comets are closer to spherical, while low mass ones are likely to be highly irregular.)
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 12006
Joined: Sat May 29, 2010 5:33 am

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Ann » Sun Nov 28, 2021 8:32 pm

Comet 67P Churyumov Gerasimenko ESA Rosetta outlined.png

It sure looks like a mythical beast of some sort!

Attack on the left, surrender at right. I mean, you can see the two heads, right?

Ann
You do not have the required permissions to view the files attached to this post.
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by neufer » Sun Nov 28, 2021 8:38 pm

Chris Peterson wrote: Sun Nov 28, 2021 4:18 pm
E Fish wrote: Sun Nov 28, 2021 3:54 pm
and even a jump from the cliff survivable.
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff. :shock:
From the base, a jump of less than a meter per second would take you right to the top, and then you'd fall back down, landing at that same low speed. (FWIW, you hit the ground at about 1 m/s when you fall from a height of 5 cm!)
Click to play embedded YouTube video.
:arrow: Astronaut John Young (commander of the Apollo 16 lunar landing mission) was able to leap about a foot above an object with 73.5 billion (=[4190]3) times the mass of 'Cherry-Geary' and survived the fall back intact.

Ergo: He could have lept about 4190 feet high on 'Cherry-Geary' and survived the fall back (assuming he misses the flag pole).
Art Neuendorffer

How craggy

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by How craggy » Sun Nov 28, 2021 11:45 pm

At last, an alien landscape that looks like an alien landscape.

Image

Newtownian
Asternaut
Posts: 7
Joined: Sun Jun 21, 2009 12:06 am

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Newtownian » Mon Nov 29, 2021 6:56 am

Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape?

Related to this is there any particular reason why we have seen at least two of these rubble residues take on a near Octahedral shape instead of one of the other polyhedrons? Might we expect to see other Platonic solid rubble balls in the future? depending on spin v. gravity.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by neufer » Mon Nov 29, 2021 1:32 pm

Click to play embedded YouTube video.
Newtownian wrote: Mon Nov 29, 2021 6:56 am
Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape? Related to this is there any particular reason why we have seen at least two of these rubble residues take on a near Octahedral shape instead of one of the other polyhedrons? Might we expect to see other Platonic solid rubble balls in the future? depending on spin v. gravity.

Art Neuendorffer

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by neufer » Mon Nov 29, 2021 1:36 pm

Click to play embedded YouTube video.
How craggy wrote: Sun Nov 28, 2021 11:45 pm
At last, an alien landscape that looks like an alien landscape.

Image
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 16596
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: A High Cliff on Comet... (2021 Nov 28)

Post by Chris Peterson » Mon Nov 29, 2021 1:38 pm

Newtownian wrote: Mon Nov 29, 2021 6:56 am Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape?
It's already a rubble pile. Just how much the shape will change depends on how much of that rubble consists of volatiles.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com